REGIOSELECTIVE INTRODUCTION OF FUNCTIONAL-GROUPS IN ALPHA-DIIMINES BYMEANS OF DIALKYLZINC COMPOUNDS - SYNTHESIS OF FUNCTIONALIZED 2-PYRROLIDINONE AND 3-PYRROLIDINONE DERIVATIVES

Alkylation of the 1,4-diaza-1,3-butadiene t-BuN--CH-CH=Nt-Bu (t-BuDAB) by functionally substituted diorganozinc compounds Zn[(CHR1)(CH2)nXR2 ]2 (n = 1-3, R1 = H, Me, XR2 = OMe, OBn, SEt, NMe2, COOEt) occurs regi oselectively. Alkylation occurs at the nitrogen atom of the N=C-C=N sk eleton of t-BuDAB when primary diorganozinc compounds are used (R1 = H ), but at the carbon atom when secondary and benzylic diorganozinc com pounds are employed. The functional groups in the diorganozinc reagent s proved to be important for the alkylation reaction only in the case of Zn[(CH2)3NMe2]2 (7) and Zn(C6H4CH2NMe2-2)2 (16), in which the stron gly coordinating NMe2 groups give either a decrease of the alkylation rate (7), or no reactivity at all (16). When t-BuDA-B is reacted with Zn[(CH2)2COOEt]2 (10) alone, a 3-pyrrolidinone (10c) is formed, wherea s the same reaction with a mixture of 10 and ClZn(CH2)2COOEt affords a 2-pyrrolidinone (10b). The reactions involve a two-step process invol ving prior regioselective introduction of the alkyl group either at th e N or C atom of an imine unit followed by an intramolecular nucleophi lic substitution leading to 10b or 10c, respectively. The molecular st ructure of 10c shows the functionalized heterocycle to be part of a co njugated enamine system.